Page 1 of 3 Eye Care Adults Anatomy of the eye Demonstrated by Lynn Ring, Ophthalmic Nurse Specialist, Epsom & St Helier University Hospitals NHS Trust ©2015 Clinical Skills Limited. All rights reserved Do not undertake or attempt any procedure unless you are, or have supervision from, a properly trained, experienced and competent person. Always first explain the procedure to the patient and obtain his/her consent, in line with the policies of your employer or educational institution Structures of the anterior eye A basic knowledge of anatomy is necessary to be able to examine the eyes effectively. Cornea The cornea is clear, to allow unobstructed passage of light, and convex, to bend and focus light rays on to the retina. It is highly sensitive, to protect the eye from intraocular invasion. The cornea has five layers. It is kept transparent by the sodium pump within the endothelial (inner) layer–when this pump breaks down, the stromal (middle) layer becomes waterlogged and loses transparency. The corneal epithelium is the only layer of the cornea to regenerate following damage. The cornea is only 0.6mm thick centrally, with 1.0mm thickness peripherally. Crystalline lens The lens sits in the posterior chamber, behind the iris and in front of the vitreous (posterior cavity). Like the cornea, it is a transparent structure which is biconvex and avascular. It is supported by suspensory ligaments called zonules that arise from the ciliary processes. The lens changes shape during ‘accommodation’—the action of viewing either near or distant objects. The ciliary muscles contract and relax, making the lens either spherical for near vision or elongated during distance vision. The lens grows more solid in people older than 45 years, gradually losing its ability to change shape, which affects near vision. This condition, called presbyopia, explains why spectacles are required for reading. Pupil The iris controls the amount of light entering the eye through the pupil by causing a ring of smooth muscle fibres around the pupil to constrict in bright light; conversely, the pupil dilates in dim light by the contraction of the radial smooth muscle in the iris. Iris The iris is the coloured part of the eye. The iris is made up of muscle fibres that control the central aperture, which is known as the pupil. Conjunctiva The conjunctiva comprises: The palpebral conjunctiva, which lines the inner eyelids; The bulbar conjunctiva, which covers the entire sclera (the white of the eyeball) from the cornea back to the optic nerve; The superior and inferior fornices, where the palpebral conjunctiva gently folds back to form the bulbar conjunctiva. To allow for easy movement of the eyeball, the conjunctiva is loosely attached, especially within the fornices where it forms folds. Anterior chamber Behind the cornea, and in front of the iris, is the anterior chamber which is filled with aqueous humour, a clear fluid produced by the ciliary body to nourish the cornea and maintain the intraocular pressure.